Effect of intermolecular anionic interactions on spin crossover of two triple-stranded dinuclear Fe(II) complexes showing above room temperature spin transition.

Two new Fe(II)-based dinuclear triple helicates having the formula {[Fe 2 (L) 3 ]·(CF 3 SO 3 ) 4 ·6.5H 2 O·CH 3 OH} (complex 1) and {[Fe 2 (L) 3 ]·(ClO 4 ) 4 ·7H 2 O·1.35CH 3 OH} (complex 2), displaying near room temperature spin transition have been synthesized and the effect of intermolecular interactions and co-operativity between metal centers on the spin crossover (SCO) has been studied. Picolinimidamide-based ligand system is chosen to provide maximum intermolecular interactions. Variable-temperature single crystal X-ray diffraction (SCXRD), magnetic study, and Hirshfeld analysis reveal that complex 1 shows a multistep spin transition, whereas, complex 2 shows an abrupt spin transition from [LS-LS] ↔ [HS-HS]. In complex 2 the presence of perchlorate anion induces high intermolecular O-H interaction that enhances the cooperativity resulting in high T 1/2 of 330 K. This study accentuates the interplay between anion effect, crystal packing, and supramolecular interactions in tuning the magnetic properties of SCO compounds.